The present invention relates generally to turbine engines and more particularly to a variable geometry inlet guide vane.
Some gas turbine engines, particularly gas turbine engines for military aircraft, include variable geometry inlet guide vanes positioned in front of the compressor inlet or in front of the fan. The inlet guide vanes each include a fixed strut having a leading edge and a trailing edge. A flap is positioned with its leading edge behind the trailing edge of the strut. The flap is pivotable about an axis near its leading edge such that the flap is pivotable from a zero deflection position to a fully deflected position. In the zero deflection position, the leading edge and trailing edge of the flap are substantially aligned with and masked behind the leading edge and the trailing edge of the strut. In the fully deflected position, the flap extends at an angle (e.g. 45°) relative to the strut, with the leading edge of the flap adjacent the trailing edge of the strut and the trailing edge of the flap is deflected substantially into the airflow, such that a side surface of the flap deflects airflow into the engine.
Generally, the zero deflection position is used during high speeds, while the fully deflected position is used during engine start up. Thus, many prior designs have been optimized only for the zero deflection position without much consideration of the inlet guide vane in the deflected position. As a result, the known inlet guide vanes may cause separation of the air flow from the flap, which results in a turbulent and even pulsating flow into the engine. This increases wear on the components downstream of the inlet guide vane. In part, some of the problems in the known inlet guide vanes occur because of the gap between the trailing edge of the strut and the leading edge of the flap. Air flowing into the gap loses momentum and then flows out unevenly, disrupting the air flow on the surface of the flap.
Sometimes it is desirable to have an exit turning angle that is positive at the outer end and negative at the inner end of the flap at the zero deflection position. This exit angle is in the form of some prescribed inlet angle distribution along the span of a downstream airfoil. Some known flaps have a camber that varies along its span, such that the camber of the flap switches from negative (at the inner end) to positive (at the outer end). This type of flap may have trouble when the flap is deflected to a closed position, where the outer end has positive camber in the direction of flap deflection while the inner end has negative camber opposite to the direction of flap deflection. This can lead to high losses and flow separations.